fix: quit after Chromium is fully started (#21488)

* fix: quit when chromium is fully started

* test: remove hacks on app.quit

* chore: RunUntilIdle is unnecessary

spec-main/fixtures/api/leak-exit-webcontentsview.js

@@ -3,5 +3,5 @@ app.on('ready', function () {
   const web = webContents.create({})
   new WebContentsView(web)  // eslint-disable-line
 
-  process.nextTick(() => app.quit())
+  app.quit()
 })